Propellant containing conjugated diene polymers reacted with at least 10% of aliphatic mercaptan

ABSTRACT

1. AN IMPROVED SOLID PROPELLANT COMPRISING INORGANIC OXIDIZING SALT AND BINDER WHICH IS PREDOMINANTLY A CURED RUBBERY POLYMER CONTAINING A MAJOR AMOUNT OF COMBINED CONJUGATED DIENE HAVING 4 TO 12 CARBON ATOMS, SAID POLYMER BEFORE CURING HAVING AT LEAST 10 PERCENT OF ITS DOUBLE BONDS REACTED WITH ALIPHATIC MERCAPTAN OF FROM 1 TO 16 CARBON ATOMS.

United States Patent 3,783,055 PROPELLANT CONTAINING CONJUGATED DIENEPOLYMERS REACTED WITH AT LEAST 10% 0F ALIPHATIC MERCAPTAN William B.Reynolds, Excelsior, Mum, and John E.

Mahan, Bartlesville, 0kla., assignors to Philhps Petroleum Company NoDrawing. Filed June 20, 1960, Ser. No. 37,516

Int. Cl. C06d /06 US. Cl. 14919.9 17 Claims This invention relates toimproved solid propellants and to their method of preparation.

Solid propellants for the propulsion of reaction engines are becomingmore and more important as the rocket field develops. One type of solidpropellant that has received considerable attention is a composite oforganic material, which serves as fuel and binder, and a solid oxidantsuch as ammonium nitrate. Propellant grains are prepared from suchmaterials by various molding techniques and the completed grain must becapable of withstanding considerable stress and shock over broadtemperature ranges. Solid propellants must be able to Withstand stressesat temperatures as low as 70 F. and it is important that the propellantgrain be improved in its low temperature tensile properties,particularly elongation.

We have discovered a method of making an improved solid propellantsuitable for fabrication of propellant grains. The propellant of ourinvention has satisfactory tensile strengths over a broad temperaturerange of 70 to +70 F. and is unexpectedly improved with respect toelongation at temperatures of 40 to 70 F. The propellant of ourinvention employs a conventional oxidant and the binder is a conjugateddiene polymer which has at least 10 percent of its double bonds reactedwith aliphatic mercaptan. In the preparation of this propellant thealiphatic mercaptan is reacted with the conjugated diene polymer andthen the polymer is cured in admixture with the oxidant.

It is an object of our invention to provide an improved solidpropellant. Another object is to provide a method of improving the lowtemperature properties of a solid propellant which employs a conjugateddiene polymer in the binder. Still another object is to provide a solidpropellant which can be formed from castable liquid polymers withimproved low temperature elongation. Other objects, advantages andfeatures of our invention will be apparent to those skilled in the artfrom the following description and claims.

The solid propellants of our invention comprise basically an oxidantplus a rubbery binder. Generally, the oxidant is an inorganic oxidizingsalt such as an alkali metal or ammonium salt of nitric or perchloricacids. Examples of suitable oxidants are ammonium perchlorate, ammoniumnitrate, sodium perchlorate, potassium nitrate, and the like. By alkalimetal we mean to include lithium, sodium, potassium, rubdidium, andcesium. Mixtures of these oxidants are also suitable. Preferably whenmixtures of the oxidizers are utilized, one of the perchlorates is in amajor proportion. The oxidizer should be ground to about 1 to 200microns average particle size and preferably to an average particle sizeof about 40 to 60 microns. The amount of oxidizing salt used withrespect to the total base composition, i.e., oxidizer plus binder, isusually about 70 to 90 weight percent.

The binder which can be used in the propellant of the invention canbroadly be any polymer of a conjugated diene wherein the conjugateddiene comprises a major portion of the polymer. Such polymers can rangefrom rubbery materials to liquids which are curable to the solid state.When the binder is a solid the propellant composition can be mixed on aroll mill or in an internal mixer such as a Banbury. The binder forms acontinuous phase with the oxidizer being a discontinuous phase in thefinished propellant. After mixing, any suitable technique such asextrusion, compression molding, and the like can be employed to form thepropellant grain. We prefer to practice our invention with castableliquid polymers such as described in the copending application of P. S.Hudson and C. C. Bice, Ser. No. 829,462, filed July 24, 1959.

The amount of binder employed in the propellant is broadly about 5 to 40parts by weight per parts of the base propellant and preferably about 10to 30 parts by weight. In addition to the base propellant, whichcomprises oxidant and binder, other materials such as one or morereinforcing agents, plasticizers, wetting agents, anti-oxidants, and thelike can be used. In some instances it is desirable to use avulcanization accelerator, a vulcanizing agent such as sulfur or anaccelerator activator such as zinc oxide. Various reinforcing agentswhich are sometimes employed include carbon black, wood flour, lignin,and various reinforcing resins such as styrene-divinylbenzene polymer,acrylic acid-styrene-divinylbenzene polymer, and the like. Also otherrubbery materials normally used as propellant binders can be admixed inminor amounts with the materials modified according to our invention inorder to make up the total binder composition.

As stated above, any polymer which is formed predominantly fromconjugated dienes and is liquid, semisolid or solid can be employed toform the propellant. Among the solid polymers we prefer those having aMooney value (ML-4 at 212 F.) less than 100 and more preferably lessthan 60.

The polymer forming the binder can be a homopolymer or copolymer ofconjugated dienes having from 4 to 12 carbon atoms and preferably 4 to 8carbon atoms per molecule. Examples of suitable conjugated dienes are1,3- butadiene, isoprene, piperylene, methylpentadiene, Z-ethyl-1,3-butadiene, phenyl-butadiene, 3,4-dimethyl-l,3-hexadiene,4,5-diethyl-1,3-octadiene, and the like. In addition, conjugated dienescontaining reactive substituents along the chain can also be employed,such as for example, halogenated dienes, such as chloroprene,fluoroprene, and the like. Of the conjugated dienes the preferredmaterial is butadiene, with isoprene and piperylene also beingespecially suitable. Copolymers of these conjugated dienes withcopolymerizable monomers containing a vinylidene (CH =C) group can beused with the conjugated diene in a major proportion. Preferably thesecomonomers contain less than 20 carbon atoms per molecule. Examples ofsuitable comonomers are aryl-substituted olefins, such as styrene,various alkyl styrenes, paramethoxystyrene, vinylnaphthalene,vinyltoluene, and the like; heterocyclic nitrogen-containing monomers,such as vinylcarbazole or pyridine and quinoline derivatives containingat least one vinyl or alphamethylvinyl group, such as 2-viny1pyridine,3-vinylpyridine, 4-vinylpyridine, 3-ethyl-5-vinylpyridine,Z-methyl-S-vinylpyridine, 3,5-diethyl 4 vinylpyridine,2-isopropenylpyridine, 2-vinylquinoline, and the like; similar monoanddi-substituted alkenyl pyridines and the like quinolines; acrylic acidesters, such as methyl acrylate, ethyl acrylate and the like; alkacrylicacid esters, such as methyl methacrylate, ethyl methacrylate, propylmethacrylate, ethyl ethacrylate, butyl methacrylate and the like; aswell as other vinylidene-containing compounds such as methyl vinylether, vinyl chloride, vinylidene chloride, vinylfuran, vinylacetylene,acrylonitrile, and the like.

The preferred polymers which are used in our improved propellants arethose which contain functional acid groups within the polymer molecule.Such polymers can be described as including terminally reactive polymershaving the formula QY wherein Q comprises the conjugated diene polymerof the type described above, Y is an acidic group and n is at least 1and preferably 2 to 4. Also included within this preferred group ofpolymers are copolymers of a major proportion of conjugated diene withcopolymerizable carboxylic acids having a maximum of 36 carbon atoms,from 1 to 5 double bonds, and 1 to 2 carboxy groups.

The polymers containing terminal acidic groups can be prepared bycontacting the monomer or monomers to be polymerized with an organoalkali metal compound, preferably an organo polyalkali metal compound.The organo alkali metal compounds contain at least 1 and preferably from2 to 4 alkali metal atoms, and those containing 2 alkali metal atoms aremore often employed. As will be explained hereinafter, lithium is thepreferred alkali metal.

The organo alkali metal compounds can be prepared in several ways, forexample, by replacing halogens in an organic halide with alkali metals,by direct addition of alkali metals to a double bond, or by reacting anorganic halide with a suitable alkali metal compound.

The organo alkali metal compound initiates the polymerization reaction,the organo radical being incorporated in the polymer chain and thealkali metal being attached terminally to at least one end of thepolymer chain. When employing polyalkali metal compounds an alkali metalis attached terminally at each end of the polymer chain. The polymers ingeneral will be linear polymers having two ends; however, polymerscontaining more than two ends can be prepared within the scope of theinvention.

While organo compounds of the various alkali metals can be employed incarrying out the polymerization, by far the best results are obtainedwith organolithium compounds which give very high conversions to theterminally reactive polymer. With organo compounds of the other alkalimetals, the amount of monoterminally reactive polymer, that is, polymerhaving alkali metal at only one end of the chain is substantiallyhigher. The alkali metals, of course, include sodium, potassium,lithium, rubidium, and cesium. The organic radical of the organo alkailmetal compound can be an aliphatic, cycloaliphatic or aromatic radical.For example, mono-, diand polyalkali metal substituted hydrocarbons canbe employed including methyllithium,

n-butyllithium, n-decyllithium,

phenyllithium, naphthyllithium, p-tolyllithium, cyclohexyllithium,4-butylphenylsodium, 4-cyclohexylbutylpotassium, isopropylrubidium,4-phenylbutylcesium, 1,4-dilithiobutane, 1,5-dipotassiopentane,1,4-disodio-2-methylbutane, 1,6-dilithiohexane, 1,10-dilithiodecane,1,lS-dipotassiopentadecane, 1,20-dilithioeicosane, 1,4-disodio-2-butene,1,4-dilithio-2-methyl-Z-butene, 1,4-dilithio-2-butene,1,4-dipotassio-2-butene, dilithionaphthalene, disodionaphthalene,4,4'-dilithiobiphenyl, disodiophenanthrene, dilithioanthracene,1,2-dilithio-1,1-diphenylethane, 1,2-disodio-1,2,3-triphenylpropane,

. 1 ,Z-dilithi o-l,Q-diphenylethane, I

1,2-dipotassiotriphenylethane, 1,2-dilithiotetraphenylethane,1,Z-dilithio-l-phenyl-l-naphthylethane,1,2-dilithio-1,2-dinaphthylethane, 1,2-disodioll-diphenyl-Z-naphthylethane, 1,2-dilithiotrinaphthylethane,1,4-dilithiocyclohexane, 2,4-disodioethylcyclohexane,3,5-dipotassio-n-butylcyclohexane, 1,3,S-trilithiocyclohexane,

1-lithio-4- 2-lithiomethylphenyl) butane,1,2-dipotassio-3-phenylpropane, 1,2-di(lithiobutyl)benzene,l,3-dilithio-4-ethylbenzene, 1,4-dirubidiobutane,

1,8-dicesiooctane, 1,5,l2-trilithiododecane, 1,4,7-trisodioheptane,

1,4-di 1,2-dilithio-2-phenylethyl) benzene, l2,7,S-tetrasodionaphthalene,

1 4,7, l0-tetrapotassiodecane,

1 5-dilithio-3-pentyne,

1 8-disodio-5-octyne,

l 7-dipotassio-4-heptyne, 1,10-dicesio-4-decyne, and

1,1 l-dirubidio-S-hendecyne, 1,2-disodio-1,2-diphenylethane,dilithiophenanthrene, l,2-dilithiotriphenylethane,l,2-disodio-1,1-diphenylethane, dilithiomethane,1,4-dilithio-l,1,4,4-tetraphenylbutane,1,4-dilithio-1,4-dinaphthylbutane,

and the like.

While the organo alkali metal initiators in general can be employed,certain specific initiators give better results than others and arepreferred in carrying out the preparation of the terminally reactivepolymers. For example, of the condensed ring aromatic compounds thelithiumanthracene adduct is preferred, but the adducts of lithium withnaphthalene and biphenyl can be employed With good results. Of thecompounds of alkali metals with polyaryl-substituted ethylenes, thepreferred material is 1,2-dilithio-1,2-diphenylethane (lithium-stilbeneadduct).

Ordinarily the dilithio compounds are preferred as being more effectivein promoting the formation of terminally reactive polymers. The polymersthus formed are especially -well suited for use in our invention asbinders for castable rocket propellant mixtures since such materials canbe cured from the liquid state to rubbery solids. The organo dialkalimetal compounds which have been set forth as being preferred, are thosewhich when prepared contain a minimum of the monoalkali metal compound.

The amount of initiator which can be used will vary depending on thepolymer prepared, and particularly the molecular weight desired. Usuallythe terminally reactive polymers which are liquids have molecularWeights in the range of 1000 to about 20,000. Depending upon themonomers employed and the amount of initiator used, semi-solid and solidterminally reactive polymers can be prepared. Usually the initiator isused in amounts between about 0.25 and about millimoles per 100 grams ofmonomer.

Preparation of the polymers containing terminal alkali metal atoms isgenerally carried out in the ramp of between 100 and C., preferablybetween 75 and +75 C. The particular temperatures employed will dependon both the monomers and the initiators used in preparing the polymers.For example, it has been found that the organolithium initiators providemore favorable results at elevated temperatures whereas lowertemperatures are required to effectively initiate polymerization to thedesired products with the other alkali metal compounds. The amount ofinitiator employed can vary but is preferably in the range of betweenabout 1 and about 30 millimoles per 100 grams of monomers. It ispreferred that the polymerization be carried out in the presence of asuitable diluent, such as benzene, toluene, cyclohexane, methylcyclohexane, xylene, n-butane, n-hexane, n-heptane, isooctane, and thelike. Generally, the diluent is selected from hydrocarbons, e.g.,parafiins, cycloparaffins, and aromatics containing from 4 to carbonatoms per molecule. As stated previously, the organodilithium compoundsare preferred as initiators in the polymerization reaction since a verylarge percentage of the polymer molecules formed contain two terminalreactive groups, and also the polymerization can be carried out atnormal room temperatures. This is not to say, however, that other organoalkali metal initiators cannot be employed; however, usually morespecialized operation or treatment is required with these materials,including low reaction temperatures. Since it is desirable to obtain amaximum yield of terminally reactive polymer, it is within the scope ofthe invention to use separation procedures, particularly with alkalimetal initiators other than lithium compounds, to separate terminallyreactive polymer from the polymer product.

The terminally reactive polymers prepared as hereinbefore set forthcontain an alkali metal atom on at least one end and preferably on eachend of the polymer chain and the organic radical of the initiator ispresent in the polymer chain. These terminally reactive polymers whentreated with suitable reagents such as carbon dioxide, sulfurylchloride, etc., and hydrolyzed provide polymers containing terminal acidgroups. The acidic groups include groups such as SOH, SO H, SO H, COOH,SeO H, SeO H, SiO T, SnO H, SbO H, SbOH, SbO H TeO H, TeO H, AsO H,AsOH, AsO H AsO H The following reactions present examples of specificmethods which can be employed to introduce the terminal acid groups. Inthese equations Q designates a polymer chain.

Reaction of terminally reactive polymer containing alkali metal atomswith the acid forming reagents can be carried out over a wide range oftemperatures, for example 75 C. to +75 C., and preferably utilizing anamount of reagent in excess of stoichiometric.

The monomers hereinbefore described for use in preparation of terminalreactive polymers containing alkali metal atoms can also be reacted withunsaturated carboxylic acids to provide liquid polymers suitable for usein carrying out the invention. Unsaturated carboxylic acids which can beemployed include acids containing up to 36 carbon atoms, from 1 to 5double bonds and 1 or 2 carboxyl groups. Also included are the so-calleddimerized acids, i.e. where two molecules of an acid are linked bydestroying one of the double bonds. Illustrative of specific acids whichcan be used are acids such as acrylic acid, methacrylic acid, itaconicacid, palmitoleic acid, oleic acid, ricinoleic acid, arachidonic acid,erucic acid, selacholeic acid, fumaric acid, maleic acid, and the like.Reaction of the monomer with the unsaturated carboxylic acid can becarried out over a wide range of temperatures depending on theparticular monomer and the particular acid employed; e.g. attemperatures between about -50 and about +100 C. The amount of acidemployed in the reaction can vary to provide polymers having an acidequivalence of from as low as 0.005 to as high as 0.2 equivalent per 100grams of polymer product.

While the polymers containing the terminal acidic groups are preferredfor the practice of the invention, polymers containing other terminallyreactive groups such as hydroxy groups or mercapto groups can beemployed. Such polymers and their preparation and curing as well asother types of terminally reactive polymers which can be used in ourinvention are described in the copending application of Carl A. Uranecket al., Ser. No. 772,167, filed Nov. 6, 1958. The liquid polymers thusformed are mixed with the oxidant and cured to solid rubberycompositions. The polymers containing carboxy groups in the molecule canbe cured with epoxides, tri(aziridinyl)phosphine oxides or sulfides.These agents can be represented by the formula X=P N (ii-Htri(l-aziridinyl)phosphine oxide, tri(2-methyl-1-aziridiny1)phosphineoxide, tri(2,3-dimethyl-1-aziridinyl)phosphine oxide,tri(2-isopropyl-1-aziridinyl)phosphine oxide,tri(2-methyl-3-ethyl-1-aziridinyl)phosphine oxide,tri(2-isopropyl-l-aziridinyDphosphine oxide,tri(2-methyl-3-n-butyl-1-aziridinyl)phosphine oxide,tri(2-hexyl-l-aziridinyl)phosphine oxide,tri(2,3-diheptyl-l-aziridinyDphosphine oxide,tri(2-methyl-3-octyl-1-aziridinyl)phosphine oxide,tri(2-ethyl-3-decyl-l-aziridinyl)phosphine oxide,tri(Z-dodecyl-l-aziridinyl)phosphine oxide,tri(2-methyl-3-tridecyl-1-aziridinyl)phosphine oxide,tri(2-ethyl-3-octadecyl-l-aziridinyl)phosphine oxide,tri(2-eicosyl-l-aziridinyl)phosphine oxide,tri(2-methyl-3-cyclopentyl-1-aziridinyl)phosphine oxide,tri(2-ethyl-3-cyclohexyl-1-aziridinyl)phosphine oxide, tri[2-n-butyl-3-(4-methylcyclohexyl) l-aziridinyl] phosphine oxide,tri(Z-phenyl-l-aziridinyl)phosphine oxide,tri(2-phenyl-3-tetradecyl-l-aziridinyl)phosphine oxide,tri(2,3-diphenyl-1-aziridinyl)phosphine oxide,tri(2-tert-butyl-3-phenyl-1-aziridinyl)phosphine oxide,tri[2-ethyl-3-(l-naphthyl) 1-aziridinyl]phosphine oxide, tri [2-r-propyl-3- (Z-naphthyl) 1-aziridinyl1phosphine 0x1 e,tri(2-methyl-3-benzyl-1-aziridinyl)phosphine oxide,tri(2-nonyl-3-benzyl-l-aziridinyl)phosphine oxide, tri [2:15-propyl-3-(2-phenylethyl) l-aziridinyl] phosphine 0x1 e, tri [2:11ethyl-3-(4-methylphenyl) 1-aziridinyl1phosphine 0x1 e,tri[2-ethyl-3-(3-n-propylphenyl-l-aziridinylJphosphine oxide, tri[2-heptyl-3- (2,4-dimethylphenyl) l-aziridinyl] phosphine oxide,tri(1-aziridinyl)phosphine sulfide, tri(Z-methyl-1-aziridinyl)phosphinesulfide, tri(2,3-dimethyl-l-aziridinyDphosphine sulfide,tri(2,3-diethyl-1-aziridinyl)phosphine sulfide,tri(2-methyl-3-isopropyl-l-aziridinyl)phosphine sulfide, tri(2-tertbutyl-l-aziridinyl)phosphine sulfide,tri(2,3-didecyl-l-aziridinyl)phosphine sulfide,tri(2-ethyl-3-pentadecyl-1-aziridinyl)phosphine sulfide,tri(2-eicosyl-l-aziridinyl)phosphine sulfide,tri(Z-methyl-B-cyclohexyhl-aziridinyl)phosphine sulfide,tri(2-pheny1-l-aziridiny1)phosphine sulfide,

7 tri(2-phenyl-3-benzyl-l-aziridinyl)phosphine sulfide,tri(2,3-dipheny1-l-aziridinyl)phosphine sulfide,tri(2-ethyl-3-phenyl-l-aziridinyl)phosphine sulfide, andtri(2-amyl-3-benzyl-1-aziridinyl)phosphine sulfide.

Suitable epoxide curatives are various commercially available epoxideresins, for example, Bisphenol A which has the general formula:

CH3 0 H ch,- H-cm-o(OoO-o-curon-cm-o) c'n.

om om-o H-cH.-o-C -h \O/ C Ha or Shell Epon X-70 1 having the generalformula:

CHFCH-CHr-CHCHz-CHCHr-(fH2 Polymers containing terminal hydroxy ormercapto groups can be cured with isocyanates. The polymers containingterminal mercapto groups can also be cured with heat alone or withdiphenyl dioxime plus magnesium oxide.

In order to improve the low temperature properties of the solidpropellant the polymer is reacted prior to curing with an aliphaticmercaptan containing from 1 to 16 carbon atoms. Preferably aliphaticmercaptans containing from 2 to 8 carbon atoms are used. Examples ofsuitable mercaptans are methyl mercaptan, ethyl mercaptan, isopropylmercaptan, butyl mercaptan, 2-methyl-3-mercapto pentane, 1mercapto-m-octane, 2-mercapto-2,3-dimethyl heptane,2-mercapto-2,4-dimethyl octane, tert-pentyl mercaptan, secondary dodecylmercaptan, 2-mercaptyl-3,4-diethyl decane, 3-mercaptyl-2-propyl-4-methyldodecane and the like.

The reaction between the polymer and the mercaptan can be readilyeffected by merely mixing the polymer and mercaptan together, generallywith a substantial excess of mercaptan. Irradiating the mixture withultraviolet light hastens the reaction. The reaction should be continueduntil at least 10 percent of the double bonds of the polymer moleculesare reacted with the mercaptan. When the polymers in which functionalgroups are present at the ends or along the polymer molecule thereaction with the mercaptan can be carried out until substantially allof the double bonds have reacted. Among the other polymers where curingis elfected across double bonds the reaction with the mercaptan shouldnot exceed about 80 percent of the double bonds available. The polymersthus reacted with the aliphatic mercaptans can be mixed with the oxidantand cured to form the propellant grain. If desired, the mercaptan can bereacted with the polymer in the presence of the oxidant with the curingagent added subsequently.

When preparing the preferred propellants of the invention employing thepolymers containing functional acidic groups within the molecule, thepolymers are admixed with the tri(aziridinyl)phosphine oxide or sulfideand the inorganic oxidizing salt, after which the mixture is suitablyincreased in temperature such that reaction occurs between the polymerand the phosphine compound to provide a solid propellant structure. Inthe preparation of the binder from liquid polymer the polymer andphosphine reactant are placed in a suitable dispersant-type mixer andthoroughly mixed for a period of 1 to 10 minutes. The oxidizer which isfinely powdered to a size in the range of from about to 200 microns isthen added and mixing is continued for a period of 15 to 45 minutesunder vacuum. During the latter mixing step the temperature is graduallyincreased to a temperature between about 100 to 300 F., preferablybetween about 150 and about 200 F. The material at this stage is aviscous slush, which is then poured into a rocket case or suitable mold.The filled mold is placed in an oven and cured for 24 to 48 hours ormore at temperatures in the range of 150 to 200 F. Semi-solid polymerscan be blended with the phosphine reactant and oxidizer and the mixtureextruded to form a curable propellant grain.

In addition to the binder and the oxidant, the propellants of thisinvention can contain a powdered metal or a metal halide. Suitablemetals are aluminum, boron, magnesium beryllium, and the like. Alloyssuch as altuninum alloys of boron, magnesium, manganese, copper, and thelike can also be used. Silicon can be utilized and the term metal isused herein to include silicon. In the propellant composition the metalcan replace part of the oxidant and the solids (oxidizer plus metal)loading can vary from to weight percent of the base with 15 to 30percent binder. The oxidizer should be 70 to 100 percent of the solidswith 0 to 30 percent as the metal. Generally the components of the solidpropellant compositions of this invention are present in the relativeamounts set forth below.

Component: Weight percent Inorganic oxidizing salt 75-85 Acidic polymer15-25 Powdered metal 0-10 In addition to other additives, burning ratecatalysts can be incorporated into the propellant composition. Thesecatalysts include materials such as ferrocyanides sold under varioustrade names, such as Prussian blue, Steel blue, Bronze blue, Turnbullsblue, Chinese blue, New blue, Antwerp blue, Mineral blue, Paris blue,Berlin blue, Hamburg blue, Williamson blue, and the like. Other usefulburning rate catalysts include copper chromite, ammonium dichromate,potassium dichromate, sodium dichromate, and the like.

To further illustrate our invention the following examples are presentedgiving conditions which should be considered as typical and not limitour invention unduly.

EXAMPLE I Polybutadiene having terminal carboxy groups and the followingproperties was treated with n-butyl mercaptan in solution under theinfluence of ultraviolet radiation. The polymer had a viscosity of 1500poises, a carboxy content of 1.82 percent and a vinyl content of about50 percent. It had been prepared in cyclohexane solvent with millimolesof lithium stilbene adduct employed as the initiator.

In reacting the polymer with the mercaptan 75 grams of polymer weredissolved in 306 grams of n-butyl mercaptan and the solution wasirradiated one hour with the light from a 100 watt mercury vapor lamp.Based on the weight increase of the recovered polymer and assumingpercent unsaturation, about 50 percent of the double bonds had reactedwith the mercaptan.

The mercaptan-treated polybutadiene containing terminal carboxy groupswas mixed with ammonium perchlorate and cured withtri(Z-methyl-l-aziridinyl)phosphine oxide to form Propellent A. As acontrol the same polymer which had not been reacted with the mercaptanwas mixed with ammonium perchlorate and cured with thetri(aziridinyl)phosphine oxide to form Propellant B. The recipes were asfollows.

Propellant A: Weight percent Carboxy-containing polybutadiene, 50% n- 9Propellant B: Weight percent Carboxy-containing polybutadiene 19.37Tri(aziridinyl)phosphine oxide 0.63

Ammonium perchlorate 80.00

The amount of curative used was on an equivalent basis of COOH in thepolymer. This goes down as the molecular weight increases as a result ofthe addition of mercaptan.

After curing for 96 hours at 160 F. the propellant compositions wereevaluated for tensile strengths at low temperatures. The results areshown in Table I.

TABLE I P.s.t. Percent l Propellant '1, F. Sm S em 1 en E, p.s.i.

1 See Method for Determining the Tensile Properties of Solid RocketPropellants, Part II, Solid Propellant Information Agency, Johns HopkinsUniversity, Silver Spring, Maryland, February 1957.

EXAMPLE II The same polymer employed in Example I was reacted with butylmercaptan until about percent of the double bonds were reacted. Thispolymer was mixed with ammonium perchlorate and cured as in Example Iwith the tri(aziridinyl)phosphine oxide according to the followingrecipe.

Weight percent Carboxy-containing polybutadiene, 15% butyl mercaptan19.47 Tri(aziridinyl)phosphine oxide .53 Ammonium perchlorate 80.00

The polymer was cured for 96 hours at 160 F. The tensile properties ofthe cured propellant are shown in Table II.

TABLE II P.s.i Percent T, F Sm S em 6 E, p.s.r

38:32:: 1,233 .2 3. 11 1 .iti- HZ KSS 'Even with only 15 percent of thedouble bonds reacted with mercaptan there is a definite improvement inlow temperature properties over the control Propellant B of Table I.

As will be evident to those skilled in the art, various modifications ofthis invention can be made, or followed, in the light of the foregoingdisclosure and discussion, without departing from the spirit or scopethereof.

We claim:

1. An improved solid propellant comprising inorganic oxidizing salt andbinder which is predominantly a cured rubbery polymer containing a majoramount of combined conjugated diene having 4 to- 12 carbon atoms, saidpolymer before curing having at least percent of its double bondsreacted with aliphatic mercaptan of from 1 to 16 carbon atoms.

2. An improved solid propellant comprising, per 100 parts of propellant,from 70 to 85 parts by weight of oxidant selected from the groupconsisting of alkali metal and ammonium salts of nitric and perchloricacids and 10 mixtures thereof and 15 to 30 parts by weight binder whichis predominantly a cured rubbery polymer containing a major amount ofcombined conjugated diene having 4 to 12 carbon atoms, said polymerbefore curing having at least 10 percent of its double bonds reactedwith aliphatic mercaptan of from 1 to 16 carbon atoms.

3. The propellant of claim 2 wherein said polymer contains at least onecarboxyl group per molecule.

4. The propellant of claim 3 wherein said polymer has been cured byreaction with a polyfunctional aziridinyl phosphine compound.

5. An improved solid propellant comprising about 70 to 90 weight percentinorganic oxidizing salt and about 10 to 30 weight percent binder whichis predominantly a polymer formed by reacting an aliphatic mercaptan ofl to 16 carbon atoms with at least 10 percent of the double bonds of aconjugated diene polymer selected from the group consisting ofhomopolymers of conjugated dienes having 4 to 12 carbon atoms andcopolymers of a major proportion of said conjugated dienes withcopolymerizable vinylidine-containing monomers, said polymer containingat least 1 acidic group per molecule, and subsequently cured inadmixture with said oxidizing salt with a reactant material having theformula wherein X is selected from the group consisting of oxygen andsulfur, P is phosphorus, the Rs are radicals containing up to a total of20 carbon atoms selected from the group consisting of hydrogen, alkyl,cycloalkyl, aryl, alkaryl, and aryl radicals, and the Rs can be unlike.

6. The propellant of claim 5 wherein said conjugated diene polymer is aliquid polymer having the formula QY wherein Q comprises a polymer ofvinylidine-containing monomers, Y is a terminal acidic group and n is aninteger of 1 to 4.

7. The propellant of claim 5 wherein said conjugated diene polymer is acopolymer of vinylidine-containing monomers with unsaturated carboxylicacids having a maximum of 36 carbon atoms, from 1 to 5 double bonds andfrom 1 to 2 carboxyl groups.

8. An improved solid propellant comprising about 70 to weight percentinorganic oxidizing salt and 15 to 30 weight percent binder which beforecuring is a liquid polymer of butadiene, said polymer containingterminal carboxy groups with at least 10 percent of the double bonds ofsaid polymer reacted with aliphatic mercaptans of 2 to 8 carbon atoms,and said polymer having been cured by reaction with a reactant materialhaving the formula E... a- I:

wherein X is selected from the group consisting of oxygen and sulfur, Pis phosphorus, the Rs are radicals containing up to a total of 20 carbonatoms selected from the group consisting of hydrogen, alkyl, cycloalkyl,aryl, alkaryl, and aryl radicals, and the Rs can be unlike.

9. The propellant of claim 8 wherein said reactant material istri(aziridinyl)phosphine oxide.

10. An improved solid propellant comprising about 70 to 85 weightpercent inorganic oxidizing salt and 15 to 30 weight percent binderwhich is a copolymer of butadiene in major amount and acrylic acid withat least 10 percent of the double bonds of said polymer reacted withaliphatic mercaptans of 2 to 8 carbon atoms, and said polymer havingbeen cured by reaction with a reactant material having the formulawherein X is selected from the group consisting of oxygen and sulfur, Pis phosphorus, the Rs are radicals containing up to a total of 20 carbonatoms selected from the group consisting of hydrogen, alkyl, cycloalkyl,aryl, alkaryl, and aryl radicals, and the Rs can be unlike.

11. An improved solid propellant comprising 70 to 85 Weight percentammonium perchlorate and 15 to 30 weight percent butadiene polymerhaving terminal carboxyl groups and at least 20 percent of its doublebonds reacted with butyl mercaptan and cured with tri(aziridinyl)phosphine oxide.

12. A method of forming a solid propellant composition having improvedlow temperature properties which comprises reacting an aliphaticmercaptan of l to 16 carbon atoms with at least 10 percent of the doublebonds of an saturated polymer containing a major amount of combinedconjugated diene having 4 to 12 carbon atoms per molecule, mixing thereaction product with inorganic oxidizing salt and curing the resultingmixture.

13. A method of forming a solid propellant composition having improvedlow temperature properties which comprises reacting an aliphaticmercaptan of 1 to 16 carbon atoms with at least 10 percent of the doublebonds of an unsaturated polymer containing a major amount of combinedconjugated diene having 4 to 12 carbon atoms per molecule, said polymercontaining at least one carboxyl group per molecule, mixing 15 to 30parts by weight of the resulting polymer with 70 to 85 parts by weightof oxidant selected from the group consisting of alkali metal andammonium salts of nitric and perchloric acids and mixtures thereof, andcuring the resulting mixture by reacting said polymer with apolyfunctional(aziridinyl) phosphine compound.

14. A method of forming a solid propellant composition having improvedlow temperature properties which comprises reacting an aliphaticmercaptan of 1 to 16 carbon atoms with at least 10 percent of the doublebonds of a conjugated diene polymer selected from the group consistingof homopolymers of conjugated dienes having 4 to 12 carbon atoms andcopolymers of a major proportion of said conjugated dienes withcopolymerizable vinylidine-containing monomers, said polymer containingat least 1 acidic group per molecule, mixing about 10 to 30 parts byweight of the polymer-mercaptan reaction product with about to 90 partsby weight of inorganic oxidizing salt, and curing the resulting mixtureby reacting said polymer with a reactant material having the for- V mulawherein X is selected from the group consisting of oxygen and sulfur, Pis phosphorus, the Rs are radicals containing up to a total of 20 carbonatoms selected from the groupconsisting of hydrogen, alkyl, cycloalkyl,aryl, alkaryl, and aryl radicals, and the Rs can be unlike.

15. The method of claim 14 wherein said conjugated diene polymer is aliquid polymer having the formula QY wherein Q comprises a polymer ofvinylidine-containing monomers, Y is a terminal acidic group and n is aninteger of 1 to 4.

16. The method of claim 14 wherein said conjugated diene polymer is acopolymer of vinylidine-containing monomers with unsaturated carboxylicacids having a 'maximum of 36 carbon atoms, from 1 to 5 double bonds andfrom 1 to 2 carboxyl groups.

17. A method of forming a solid propellant composition having improvedlow temperature properties which comprises reacting butyl mercaptan withat least 20 percent of the double bonds of butadiene polymer havingterminal carboxyl groups, and curing 15 to 30 parts by weight of theresullting polymer in admixture with 70 to parts by weight of ammoniumperchlorate by reaction with tri(aziridinyl) phosphine oxide.

References Cited UNITED STATES PATENTS 2,931,437 4/1960 Smith 149-192,877,504 3/1959 Fox 149-19 BENJAMIN R. PADGETT, Primary Examiner US.Cl. X.R. l49-20, 22

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,783,055 William B. Reynolds et a1. Dated January I It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column ll, line 25, "an saturated" should read an unsaturated Signed andsealed this 23rd day of" April 197A.

(SEAL) Attest:

EDWARD rLFLET-GLEILJR. C MARSHALL DANN Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,783,055 William B. Reynolds et a1. Dated January I It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column ll, line 25, "an saturated" should read an unsaturated Signed andsealed this 23rd day of" April 197A.

(SEAL) Attest:

EDWARD rLFLET-GLEILJR. C MARSHALL DANN Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,783,055 William B. Reynolds 91; al. Dated January 1,

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 11, line 25, "an saturated" should read an unsaturated Signed andsealed, this 23rd day of April 19% (SEAL) Attest:

EDWARD M.FLETGHER,JR. C MARSHALL DANN Commissioner of Patents AttestingOfficer

1. AN IMPROVED SOLID PROPELLANT COMPRISING INORGANIC OXIDIZING SALT ANDBINDER WHICH IS PREDOMINANTLY A CURED RUBBERY POLYMER CONTAINING A MAJORAMOUNT OF COMBINED CONJUGATED DIENE HAVING 4 TO 12 CARBON ATOMS, SAIDPOLYMER BEFORE CURING HAVING AT LEAST 10 PERCENT OF ITS DOUBLE BONDSREACTED WITH ALIPHATIC MERCAPTAN OF FROM 1 TO 16 CARBON ATOMS.